Positioning device, especially for offset plates

ABSTRACT

The invention relates to a device for positioning an element with respect to at least two reference points ( 4   a   , 4   c ), in which said device acts upon a working point on the element to be positioned and comprises a positioning arm attached to a fixed hinging point with respect to said reference points ( 4   a   , 4   c ), comprising two mutually hinged parts ( 6   a   , 6   b ) allowing a movement of said element to each reference point ( 4   a   , 4   c ). The invention related further to a device for positioning at least one offset plate on a positioning table of a pre-press equipment, comprising means to move the offset plate in a plane parallel to the positioning table to at least one reference point ( 4   a ) on the positioning table, in which said means acts upon a working point situated in the supporting plane of the offset plate on the positioning table.

This application claims the benefit of International Application No.PCT/EP02/04848 filed Apr. 26, 2002.

BACKGROUND OF THE INVENTION

The invention relates to a device for positioning at least one offsetplate on a positioning table of a pre-press equipment, comprising meansto move the offset plate in a plane parallel to the positioning table toat least one reference point on the positioning table, in which saidmeans act upon a working point situated in the supporting plane of theoffset plate on the positioning table, in which said means act upon aworking point situated in the supporting plane of the offset plate onthe positioning table and wherein said means act upon said working pointthrough an aperture in the positioning table.

For the positioning of at least one offset plate on a positioning tableof a pre-press equipment, devices are known in which the offset platesare put on the positioning table by means of a loader in the vicinity ofthree roller shaped reference points. The offset plate is positionedwith respect to these three rollers by means of three fingers which areplaced facing the rollers and which push the offset plate against theserollers. Once there is contact between the offset plate and the threerollers, the plate is positioned and the plate is kept in its correctposition by means of vacuum channels.

These devices has the disadvantage that different positioning tableswith different equipment are necessary to position offset plates withdifferent sizes. The positioning system is in that way dependent on thesize of the offset plates.

A further disadvantage is that different means are necessary to performthe different movements to the reference points.

A solution to these disadvantages can be found in U.S. Pat. No.4,790,584, in which a compliant linkage apparatus for providing, in asingle stage, three degrees of freedom in a single plane. The apparatuscomprises an upper plate, a lower plate under the upper plate, slidingmeans for allowing the upper and lower plates to slide relative to eachother in X, Y, and theta, and orientation means for causing plates toattract each other in a particular orientation to resiliently resistrelative lateral and rotational displacements of the plates. The deviceincludes vacuum engagement members which are connected to a vacuum platefor engaging and disengaging the workpiece.

The problem with this apparatus is that it is not applicable on printingplates. The aluminium printing plates have thickness of 0.1 to 0.3 mm.Because of the fact that in this apparatus the workpiece is engaged anddisengaged at its top surface through vacuum engagement members, whenusing printing plates, these printing plates will bend and it is verydifficult to get them flat on the supporting surface. Furthermore, theupper layer of the printing plates consist of a very photosensitiveemulsion layer, which will be damaged when sucking the printing platesat their top to the vacuum engagement members.

In DE 22 01 873, a device is described for positioning a printing platewhich is susceptible for being held in a movable manner by means of atightening strip, and provided with marking in relation to thecylindrical printing press plate holder which is arranged to receive thetightening strip of an offset press, in particular of a polychromeoffset press. There are provided reference markings which, due to thecorrect position of the printing plate, will coincide with the markingsof the printing plate, depending on which reference markings of thetightening strip can be brought into a defined position, in order totighten the printing plate in a reproducible way in a relativelyidentical position in relation to the tightening strip. In the secondembodiment of this patent application, an adjusting plate is providedwhich is slidably mounted against a ground plate through means of threemicrometer screws. Between the adjusting plate and the ground plate athree-pointed support is provided. The adjusting plate is permanentlyremained in contact with the micrometer screws by means of apre-tensioned spring which on the one hand is mounted to the adjustingplate, and on the other hand is mounted to the ground plate. In thisdevice, the printing plate is moved together with the adjusting plate inrelation to the ground plate by means of the micrometer screws.

The disadvantage of this device is first of all that a complex projectorsystem is used to check when the reference markings coincide with themarkings of the printing plate. Furthermore, also a complex positioningsystem for the printing plate is provided, using an extra adjustingplate to take care of the correct position of the printing plate. It isnot the printing plate itself which is moved in order to make thereference markings coincide with the markings of the printing plate andconsequently to bring the printing in a correct position.

The purpose of the invention is to provide in a device for positioningan offset plate on a positioning table of a pre-press equipment whichdoesn't show the abovementioned disadvantages.

SUMMARY OF THE INVENTION

This purpose is achieved by providing in a device for positioning atleast one offset plate on a positioning table of a pre-press equipment,comprising means to move the offset plate in a plane parallel to thepositioning table to at least one reference point on the positioningtable, in which said means act upon a working point situated in thesupporting plane of the offset plate on the positioning table, in whichsaid means act upon a working point situated in the supporting plane ofthe offset plate on the positioning table, wherein said means act uponsaid working point through an aperture in the positioning table, whereinat least two reference points are situated on the positioning table andwherein said means comprise a positioning arm which is attached to afixed hinging point with respect to said reference points, comprisingtwo mutually hinged parts allowing a movement of said element to eachreference point.

This has the advantage that on the one hand, offset plates withdifferent sizes can be positioned by the same device and for theperforming of the movement of the offset plate to each reference pointthe same means, i.e. a positioning arm, is provided. On the other hand,the processing time of the positioning device can be shortened when itis compared with the processing time which is necessary in a positioningsystem which is attached to the loader. In the device according to theinvention, the positioning can be performed while the positioning tableis moved to the place where the offset plate is illuminated.

In a more specific embodiment of a device according to the invention,the positioning arm comprises a vacuum sucking element to make contactwith the element.

In a further more specific embodiment of a device according to theinvention, between the two mutually hinged parts a spring is provided tobring the hinged parts back into their original position after thepositioning of the element.

In a preferred embodiment of a device according to the invention, saidpositioning arm comprises a double working cylinder to perform themovement of the positioning arm.

In a more preferred embodiment of a device according to the invention,the positioning arm comprises a suction cup and a second cylinder whichprovides for an up and down movement of the suction cup.

Preferably, in a device according to the invention the positioning tableis provided with two positioning arms to position two offset plates atthe same time or to position offset plates with greater size on thepositioning table.

This has the advantage that the both positioning arms can be used topush the offset plate against the reference points.

In order to explain the properties of this invention further and inorder to specify additional advantages and distinctive features thereof,there now follows a more detailed specification of a device forpositioning an element with respect to at least two reference pointsimplemented according to this invention. More specific, a device forpositioning at least one offset plate on a positioning table of apre-press equipment will be described. It is clear that nothing in thefollowing specification may be interpreted as a restriction on theprotection claimed for this invention in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be explained on the basis of figures, whereby

FIGS. 1 a to 1 c are figures to explain the principle of the positioningarm;

FIG. 2 is a cross-sectional view of a positioning arm which is armattached to the positioning table;

FIG. 3 is a perspective view of the positioning arm as shown in FIG. 2;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The device (1) for positioning at least one offset plate (2) on apositioning table (3) of a pre-press equipment, as shown in FIGS. 1 a to1 c, comprises a loading device (not shown in the figures) which picksup the offset plate out of a cassette or a trolley, and puts the pickedup offset plates on a positioning table (3). Thereafter, the offsetplates are illuminated with a laser (not shown on the figure). Afterthis illumination process, the offset plate (2) is transported to aonline offset plate processor by means of a unloading system (not shownon the figure).

FIGS. 1 a, 1 b and 1 c show the principle for positioning the offsetplate (2) on the positioning table (3).

On the positioning table (3), three roller shaped reference points (4 a,4 b, 4 c) (hereafter called rollers) are provided. Further, apositioning arm (5) is provided to move the offset plate against therollers (4 a, 4 b, 4 c). The positioning arm (5) consists of twomutually hinged parts, i.e. a first (6 a) and a second hinged part (6b), allowing a movement of the offset plate (2) to each roller (4 a, 4b, 4 c). The first part (6 a) of the positioning arm (5) is attached toa fixed hinging point (7) which is provided to the positioning table(3). The two hinged parts (6 a, 6 b) are mutually hinged to each otherin a floating hinging point (8). The second part (6 b) of thepositioning arm (5) is provided with a vacuum sucking element (9) whichcan move in an aperture (20) (shown in FIG. 2 in the positioning table(3). In that way, the vacuum suction cup (9) can make contact with theoffset plate (2). Between the two hinged parts (6 a, 6 b) a spring (10)is provided to bring the two second hinged part (6 b) back into itsoriginal position after the positioning of the offset plate (2).

The offset plate (2) always have to be positioned against the threerollers (4 a, 4 b, 4 c) with a small tolerance of some μm. After theloading of the offset plate (2) on the positioning table (3) in thevicinity of the rollers (4 a, 4 b, 4 c), the positioning arm (5) has tosuck the offset plate (2) by means of the vacuum sucking element (9)which can move in the aperture (20) in the positioning table (3).Thereafter, a force F is exerted on the positioning arm (5), as shown inFIG. 1 b. Because of that, the positioning arm (5) will rotate aroundthe fixed hinging point (7) and the offset plate (2) is pushed ordragged with force A against the first two rollers (4 a, 4 b). Once theoffset plate (2) is positioned with respect to these two rollers (4 a, 4b), the positioning arm (5) will rotate around the fixed hinging point(7), but also around the floating hinging point (8) through which theoffset plate (2) is moved with force B in the Y-direction. In that way,the spring (10) is stretched. Once the offset plate (3) is positionedagainst the third roller (4 c), the positioning arm (5) blocks and staysin the same position. Thereafter, the offset plate (2) is sucked to thepositioning table (3) by means of vacuum channels (not shown on thefigure) through which it remains in its position. The suction cup (9)which moves the offset plate (2) is now placed in a vacuumless positionand the positioning arm (5) is moved back to its original position (asshown in FIG. 1 a) by exorting force F in the other direction.

By using this principle, two movements (A, B) in two differentdirections are performed through the same means, i.e. the positioningarm (5). Furthermore, the suction cup (9) acts upon a working pointsituated in the supporting plane of the offset plate on the positioningtable (3). The offset plate (2) is accordingly not moved throughsidewardly pushing, but is moved through sucking the underside of theoffset plate (2) and moving it to the correct position by means of thepositioning arm (5).

The movement of the positioning arm (5) (shown in detail in FIGS. 2 and3) is performed through a double working cylinder (11). While the offsetplate (2) is positioned, the cylinder (11) is retracted through whichthe positioning arm (5) can rotate around the hinging points (7, 8).After the positioning, the cylinder is pushed outwardly while the spring(not shown on the FIGS. 2 and 3) brings the hinged parts (6 a, 6 b) backinto their original position, in which a hook of 90° is formed betweenthe hinged parts (6 a, 6 b). The double working cylinder (11) is hingedattached, at one end by means of the coupling piece (12) and at theother end through a rod eye (not visible on the figure).

The positioning arm (5) is further provided with a second cylinder (13)which provides for the up and down movement of the suction cap (9). Thesuction cap (9) is coupled to the rod of the second cylinder (13) bymeans of a vacuum coupling piece (14). In this way, vacuum can beconnected to the suction cap (9). After placing the offset plate (2) inthe vicinity of the rollers, the second cylinder (13) pushes up thesuction cap (9), whereafter the suction cap is sucked vacuum and theoffset plate (2) is pushed against the rollers (4 a, 4 b, 4 c).Subsequently, vacuum channels in the positioning table (3) provide thatthe offset plate (2) stays in its correct position. Thereafter, thesuction cap (9) is put in a vacuumless condition and the second cylinder(13) moves again downwards so as to be situated under the surface of thepositioning table (3).

The freedom of movement of the positioning arm (5) is limited because ofa bearing holder (15) which can move in a stop block (16). These twoelements determine the maximum movement space of the offset plate (2) inthe X- and Y-direction and provide that the hook between the two hingedparts (6 a, 6 b) can not be smaller than 90°.

The fixed hinging point (7) is formed through two ball bearings (17), afastening bolt (18), a bearing house (19) and a fastening ring (21). Thefastening bolt (18) is screwed in in the underside of the positioningtable (3).

The floating hinging point (8) is formed through two ball bearings (22),a fastening bolt (23), a coupling ring (24), a bearing house (25), anintermediate ring (26) and a self-locking nut (27).

Normally, two positioning arms (5) are provided on the positioning table(3) as to illuminate two offset plates (2) at the same time. If offsetplates (2) with a greater size have to illuminated, there is only spacefor one offset plate (2) on the positioning table (3). To position suchoffset plates (2), both positioning arms (5) can be used to push theoffset plate (2) against the rollers (4 a, 4 b and 4 c).

1. Device for positioning at least one offset plate on a positioningtable of a pre-press equipment, comprising means to move the offsetplate in a plane parallel to the positioning table to at least onereference point (4 a) on the positioning table, in which said means actupon a working point situated in the supporting plane of the offsetplate on the positioning table, wherein said means act upon said workingpoint through an aperture in the positioning table, wherein at least tworeference points (4 a, 4 c) are situated on the positioning table andwherein said means comprise a positioning arm which is attached to afixed hinging point with respect to said reference points (4 a, 4 b),comprising two mutually hinged parts (6 a, 6 b) allowing a movement ofsaid element to each reference point (4 a, 4 c).
 2. Device according toclaim 1, wherein the positioning arm comprises a vacuum sucking elementto make contact with the offset plate.
 3. Device according to claim 2,wherein between the two mutually hinged parts (6 a, 6 b) a spring isprovided to bring the first and second hinged part (6 b) back into theiroriginal position after the positioning of the offset plate.
 4. Deviceaccording to claim 1, wherein said positioning arm comprises a doubleworking cylinder to perform the movement of the positioning arm. 5.Device according to claim 1, wherein the positioning arm comprises asuction cup and a second cylinder which provides for an up and downmovement of the suction cup.
 6. Device according to claim 1, wherein thepositioning table is provided with two positioning arms to position twooffset plates at the same time or to position offset plates with greatersize on the positioning table.